Regulating the sexual maturity of rainbow trout in food fish production

Until recently, light manipulation has only been used in year-round fry production of rainbow trout. Now light treatments have come to be regarded as a potential tool for improving the fish quality. As fish mature, their quality deteriorates. If it were possible to control the timing of maturation, more fish of an appropriate maturity status, i.e. good quality, could be produced.

The goal of the project

The goal was to study regulation of the maturation of rainbow trout (Oncorhynchus mykiss) using light treatments. The effects of light treatments on maturation and end-product quality were evaluated. The light treatments were conducted with underwater lamps within sea cages at the Rymättylä Fisheries Research Station. Based on the experimental data, a statistical model was created for annual timing and duration of light treatment to delay maturation.

Photo: Kari Ruohonen

Results

Administering light treatments with underwater lamps is a simple and cost-effective way to regulate the maturation of fish stock. Light treatments that continued from midsummer until the autumn harvest were observed to be efficient in delaying maturation and the deterioration of quality caused by maturation was efficiently prevented. For example, the fat content of the fillet, the colour of the muscle and the sensory quality of the roe and the muscles were better in fishes that had been subjected to light treatment. No negative effects in the production or quality were observed in light-treated fish when compared with control fish. Light treatments make it possible to lengthen the supply season of high quality rainbow trout. This has the potential to decrease the seasonal oversupply of raw material and attenuate price fluctuations.